- reduce ZAP_BLOCK_SIZE to 16 when vp != 0. This pushes the exit latency down to below 100 usecs on Lee Revell's box.

- added a preempt_count field to /proc/latency_trace. This makes it easier to spot IRQ contexts and generally it gives a nice overview of how the preemption depth changes. It should also help us debug those 900usec weirdnesses related to cpu_idle. (if they still occur)

- made the tcp packet-queue collapsing dependent on VOLUNTARY_PREEMPT.

- fixed 10-20 msec latencies triggered by 'netstat', which occur when there are lots of sockets on a box.